*{
    margin: 0;
    padding:0;
}

ul,ol,li{
    list-style: none;
}

img{
    display: block;
    width: 100%;
    height: 100%;
}

.box{
    width: 900px;
    display: flex;
    flex-direction: column;
    position: relative;
    margin:  50px auto;
}

.box .show{
    width: 400px;
    height: 400px;
    border: 2px solid #000;
}

.box .mask{
    width: 200px;
    height: 200px;
    background: yellow;
    opacity:.5;
    position: absolute;
    left:0;
    top:0;

    display: none ;
}

.box .list{
    width: 100%;
    flex:1;
    display: flex;
    justify-content: flex-start;
    align-items: center;
}

.box .list li{
    width: 80px;
    height: 80px;
    margin: 20px 20px;
}

.box .list li img.active{
    border:2px solid red ;
}

.box .glass{
    width: 800px;
    height: 800px;
    border: 2px solid red ;
    position: absolute;
    left:450px ;
    top:0 ;
    background-repeat: no-repeat;
    background-position: 0 0 ;
    background-size: 1600px 1600px;
    display: none ;
}